Core-drilling system

ABSTRACT

A core-drilling system comprising a novel method which accommodates disablement of an overshot for selective or controlled release of its coupling relation with spearhead or latch structure of a core barrel assembly within a drill hole when an operator pumps the wire line to which the overshot is attached, up and down a prescribed number of times.

prising a novel f an overshot for pling relation with ire line to which the overshot is attached, up and down a prescribed number of times.

I. No. 20,709

1175/58, 294/86. l 7, 294/862] lEZib 9/20 166/3 l5; 175/58, 246-248, 257; 294/86. l 7-86.22

Lyle J. Martlnsen Murray, Utah 20,709 Mar. 18, 1970 Dec. 14, 1971 Assignee Boyles Bros. Drilling Co.

Salt Lake City, Utah Original application Aug. 27, 1968, Ser. No. 778,879, now Patent No. 3,537,743, Original application Aug. 10, 1966, Se No. 571,521, now Patent No. 3,441,098.

Divided and this application Mar. 18, 1970,

CORE-DRILLING SYSTEM 3 Claims, 14 Drawing Figs.

Int.

United States Patent [72] Inventor [21'] Appl. No.

[22] Filed [45] Patented [50] FieldofSearch.................................,..........

lilii ibi 1 ii I if] Patented Dec. 14, 1971 3,627,067

4 Sheets-Sheet 1 IF'IC-ll. [FIG-.2

INVENTOR.

LYLE J. MARTI NSEN H IS AT ORNEY CORE-DRILLING SYSTEM This application is a division of U.S. Pat. application, Ser. No. 778,879, filed Aug. 27, 1968, now U.S. Pat No. 3,537,743, which was a division of U.S. Pat. application, Ser. No. 571,521, filed Aug. 10, 1966, now U.S. Pat. No. 3,441,098.

BACKGROUND Field of Invention The present invention relates generally to a novel core drilling method and more particularly to a unique method for disabling an overshot to release a core barrel assembly therefrom in a drill hole. The overshot of this invention, therefore, provides a new release feature to, under precise control of the operator, selectively accommodate unlatching and/or prevent subsequent latching to the core barrel assembly.

In core drilling, it has been customary to employ an annular drilling bit which is disposed at the distal end of outer tube carried at the distal end of a drill string and which progressively cuts through rock, responsive to rotation of the drill string, leaving an uncut, upwardly projecting rock core central of the bit. As drilling proceeds the core incrementally becomes disposed within a core-receiving barrel or inner tube of the core barrel assembly, which has been positioned in the drill string and releasably coupled with the outer tube by a latch assembly of the core barrel assembly. A swivel mechanism is interposed between the core-receiving barrel and the core barrel latch assembly so that the latch assembly normally rotates with the drill string and the core-receiving barrel normally is stationary during drilling.

When the length of core has become disposed in the corereceiving barrel sufficient to fill the barrel (usually several feet long), the drill string and/or the core barrel is displaced a short distance away from the leading end of the hole adequate to break the core from the rock formation. Afterward, the overshot, carried at the end of the wire line (cable), is latched to the spearhead of the core barrel assembly, the core barrel assembly is uncoupled from the outer tube by movement of the core barrel assembly away from the bit and the overshot and latched core barrel assembly are withdrawn, along with a broken core, from the drill string.

Use of such prior art systems has presented several significant problems, one of which is mentioned below.

Prior commercially utilized core barrel latch assemblies have conventionally contained a number of mechanical parts which have been required to mechanically move relative to each other when coupling and uncoupling the core barrel assembly from the outer tube. Such latch assemblies, under certain drilling conditions, will become sanded up" so that it is difficult, if not impossible, to cause the parts to mechanically move a sufficient distance relative to each other to uncouple the core barrel assembly from the outer tube. To release a sanded up latch assembly from the outer tube, significantly high forces are exerted on the latch assembly through the wire line and latched overshot, often resulting in shear failure of the spearhead at the distal end of the core barrel assembly. Thereafter, expensive and time-consuming techniques must be used to remove the broken core barrel assembly from the hole or to remove the entire drill string.

Moreover, the existence of the mentioned sand up condition cannot be ascertained, using prior art equipment, until after the overshot has been securely latched to the spearhead and a retraction force applied. Thereafter, unlatching of the overshot from the spear head, when necessary, is awkward, time consuming, and unreliable. The most common way of unlatching the overshot from the spearhead of the core barrel assembly is to use a split sleeve which, under certain conditions, slides over the back ends of conventional lifting dogs, which function as jaws, to thereby counterbias the dogs into an open, unlatched position. The same problem holds true when endeavoring to release the core barrel assembly for coupling with the outer tube after the core barrel assembly has been lowered into the drill string using an overshot carried at the end of a wire line. In either case, close control by the wire line operator over the placement of the split sleeve over the back ends of the lifting dogs to release the core barrel assembly from the overshot is not possible. Inadvertent unlatching of the core barrel assembly from the overshot is common place.

When the split sleeve is inadvertently actuated to bias the lifting dogs in open position and release the core barrel assembly, as when the overshot and latched core barrel assembly are being placed in a downwardly extending dry" hole or removed from a hole which deviates from being straight as is often the case, the core barrel assembly will fall with great force against and frequently break the expensive bit.

The latched condition between the overshot and core barrel assembly cannot be destroyed inadvertently, but only when the operator elects to sever the relation. This invention, thus, provides a new release feature to, under precise control of the operator, selectively accommodate unlatching and/or prevent subsequent latching of the core barrel assembly. When a wire line operator desired to release the overshot, the operator merely pumps up and down on the wire line, which is attached to the overshot, a preset number of times until the overshot becomes disposed in a disabled position and is released from the overshot.

Accordingly, the present invention is a worthwhile contribution to the core drilling art because it provides a system which substantially overcomes the above-mentioned problem of the prior art.

A principal object of this invention is the provision of a unique method wherein an overshot may be detached from a core barrel assembly under close control of the operator.

Another significant object of the present invention is the provision of a novel method for disabling an overshot so as to prevent subsequent latching between the overshot and a core barrel assembly.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary elevation shown partly in cross section of a core barrel assembly operatively coupled to the outer tube of a drill string disposed in a hole;

FIG. 2 is an elevational view similar to FIG. 1 showing the core barrel assembly uncoupled from the outer tube and being removed from the hole, along with the broken core, using an overshot which is claimed in copending U.S. Pat. application, Ser. No. 778,879;

FIG. 3 is a fragmentary cross section shown in elevation of a centrally disposed swivel mechanism of the core barrel assembly of FIG. 1;

FIG. 4 is a fragmentary cross section elevation of the outer tube-coupling spearhead-latching assembly of the core barrel assembly of FIG. 1;

FIG. 5 is a cross section in plan taken along the line 5-5 of FIG. 4;

FIG. 6 is an elevation of the overshot of FIG. 2;

FIG. 7 is an elevational cross section of the overshot of FIG. 2 taken along line 77 of FIG. 6;

FIG. 8 is a fragmentary cross section shown in elevation of the overshot of FIG. 6 shown with the plunger thereof in the retracted position and the spearhead or prong hooks, disposed at the distal end of each prong, latched to the overshot;

FIG. 9 is a fragmentary cross section similar to FIG. 8 illustrating the plunger in the extended position which (a) detaches the spearhead or prong hooks from the overshot when previously latched and (b) prevents subsequent latching of the spearhead hooks with the overshot;

FIG. I0 is a fragmentary elevation shown partly in cross section illustrating the easy mode of manual surface detachment of the overshot of FIG. 2 from the core barrel assembly of FIG. 2;

FIG. 11 is a fragmentary elevation shown partly in cross section of a second overshot shown with a plunger retracted and the overshot latched to a conventional spearhead;

FIG. 12 is a cross section in plan taken along line 12-12 of FIG. 11;

FIG. 13 is a fragmentary elevation of the overshot of FIG. I l with the plunger extended and the conventional spearhead unlatched; and

FIG. 14 is a fragmentary side elevation illustrating another overshot having modified teeth construction at the release housing.

GENERAL Reference is now made to the drawings wherein like numerals are used to identify like parts throughout. FIGS. 1 and 2 depict a core-drilling system manufactured according to the present invention and generally designated 20. Some parts of the core-drilling system 20 are conventional and some are decidedly novel. More particularly, the core-drilling system 20 comprises an outer tube 22, a bit 24, and a string of drill pipe (not shown) positioned in a downwardly extending hole 26 in the earth, all of which is conventional. The sections of the drill string are normally threadedly coupled one to another and the last section is threadedly coupled to the outer tube 22. In turn, the outer tube 22 is threadedly connected at 28 to the hollow bit 24. The bit 24 may be of any suitable type capable of drilling through rock formations, diamond bits being commonly used for this purpose.

For purposes which will subsequently become more fully understood, the outer tube 22 is provided with an upper twoway coupling annular recess 30 and a closely spaced somewhat larger lower annular recess 32.

During the drilling, as is conventional, the drill string along with the outer tube 22 and the bit 24 are rotated by conventional apparatus (not shown) causing the bit to progressively cut an annular hole in the rock, leaving an uncut rock core 36 within the hollow of the bit, which core incrementally increases in length as drilling proceeds.

As the core 36 lengthens beyond the bit 24, it is accepted within a core-receiving hollow 40 of an inner tube 38 of the core barrel assembly, generally designated 42, through the inner tube shoe 44 and a core spring 46. This also is conventional.

Once the core 36 has grown to substantially fill the inner tube 38, the outer tube 22 along with the core barrel assembly 42, is elevated slightly to bread the core as at 50 (FIG. 2). When the core is particularly soft, it may only be necessary to elevate the core barrel assembly to break the core. Thereafter, the core barrel assembly is uncoupled from the outer tube and elevated to the surface, using an overshot, in the case of this invention the novel overshot generally designated 52 (FIG. 2) is used.

The core spring 46 which rests along the inner tapered angular surface 54 of the shoe 44, is contiguous at its outer surface with the core 36. Thus, as the core barrel assembly 42 is elevated, as mentioned, the weight of the core will cause the core spring 46 to slide downward a short distance along the tapered surface 54 to be compressively wedged against the core 36 to hold the core within the barrel 40 as the core barrel assembly is elevated to the surface.

The core barrel assembly 52 also comprises a swivel mechanism, generally designated 60, which is conventional in all respects except one. The swivel mechanism 60 functions to accommodate rotation of the upper portion of the core barrel assembly with the drill string while maintaining the lower portion of the core barrel assembly, as at the inner tube, in a stationary position to receive the core and to accommodate water circulation. More particularly, as best shown in FIG. 3, the swivel mechanism 60, which is threadedly connected at 62 (FIG. I) to the inner tube 38, exteriorly comprises a bearing retainer 64 with top aperture 66 through which a bearing shaft 68 rotatably passes. The shaft 68 terminates at planar surface 70 and is retained in position by a baseplate 72 held in position by a cap screw 74 threaded into a bore (not shown) axially disposed and opening at the shaft surface 70. The retaining plate 72 confines a lower bearing assembly 76 in the illustrated operational position against a spacer 78 concentric of the shaft 68 while an upper bearing assembly 80 is interposed concentric about the shaft 68 between the spacer 78 and one ore more resilient washers 82 made of a suitable wear resistant material such as neoprene. The neoprene washers 82 rest between the upper bearing assembly 80 and an abutment face 84 of the bearing retainer 64. The swivel is conventional except for the resilient washers.

When the core is hard to break, normally the operator will pull the entire drill string a slight distance to break the core. When this happens the neoprene washers compress sufficiently to allow the shoe 44 (FIGS. 1 and 2) to contact the bit 24 so that the principal portion of the breaking load is transferred through the outer tube 22 rather than through the core barrel assembly 42.

COUPLING-SPEARI-IEAD ASSEMBLY OF FIGS. 1-5

The upper portion of swivel mechanism 60 comprises a body 90, a plurality of radially yieldably prongs or resilient fingers, generally designated 92, preferably fabricated of tool steel, and leaf spring 94, interposed between each prong 92 and the body as seen in FIGS. .1, 2, 4, and 5. While four prongs 92 are shown, it is to be appreciated that any suitable plural number could be utilized, if desired. I

The body 90, illustrated in detail in FIGS. 4 and 5, is preferably of tool steel and, in the configuration illustrated in FIG. 4, comprises a solid piece, which adds weight to the core barrel assembly and provides the solid support base for the prongs 92.

The bearing shaft 68 is threaded into a threaded bore (not shown) axially disposed in the body 90 and opening at the bottom surface 99 (FIG. 1 A locknut 101 secures the shaft 68 in such threadedly connection relation with the body 90. An open notch is provided along each of the'four side positions of the body at 90 spacings. One leaf spring 94 is securely mounted at each open notch-I00 against axial and circumferential movement by use of a pairof bolts 102 which are securely threaded into threaded bores I04. Lockwires 106 are used to prevent inadvertent loosening of the bolts 102 during use of the core barrel assembly. At the same time, the mentioned bolt mounting of each resilient leaf spring 94 to the body 90 enables essentially radial movement inward in a fish tail motion accommodated by tapered flat walls I08, one disposed immediately adjacent each leaf spring 94.

The top of the body 90 has an essentially traversely flat centrally located topsurface I10 and four inwardly tapered open grooves 112, each accommodating the mentioned radial inward yielding of the prongs 92, when the core barrel assembly is being uncoupled from the outer tube and latched to the overshot. A very close tolerance space is provided between each open groove I12 and the adjacent base surface 114 of each prong 92. Thus, when and if the prongs 92 are subjected to a downward axial force which slightly buckles the spring 94, the base surface 114 will bottom out at the adjacent groove 112 before stress on the adjacent leaf spring 94 exceeds the elastic limit. Of course, it is to be appreciated that, since the inward radial yielding of the prongs 92 approximately traverses an arcuate path, the open groove 112 could conveniently comprise a curvilinear rather than a linear surface.

A number of weldments 115 of suitable radially projecting length are integrally disposed upon the cylindrical surfaces of the body 90 so that they will have an arcuate surface adjacent the inside wall of the outer tube 22 which arcuate surface will be radially spaced very closely from the inside wall of the outer tube during drilling. In this way, any wobbling of the body 90 will not be excessive.

The spearhead latching-outer tube coupling prongs 92 are preferably fabricated from tool steel and, in the illustrated embodiment, are all of identical construction, material and dimensions. Importantly, the prongs are constructed and arranged in an array such that a hollow space is provided between to obviate sanding up problems of the type experienced by prior art core barrel assemblies when in coupled position with the outer tube. Significantly, it should be noted that the prongs use no mechanical parts which must move relative to each other during a coupling and uncoupling of the core barrel assembly. It should be kept in mind that the prongs 92 serve a twofold purpose; namely, to selectively accommodate coupling of the core barrel assembly with the outer tube and to accommodate spearhead latching to an overshot and outer tube uncoupling for retrieval of the core barrel assembly from the hole. Inadvertent unlatching or mislatching of one prong does not affect the outer tube coupling or the spearhead-latching characteristics of this invention.

Structurally, in transverse cross section, each prong 92, as shown on the right of FIG. 5, is wedged shape with an arcuate surface disposed at the exterior. As shown in FIG. 4, each prong comprises a ski or cam 130, the purpose of each cam 130 being to prevent hanging up" of the core barrel assembly within the drill string, such as on a poor tolerance lip at a threaded drill string coupling.

During the process of placing the core barrel assembly in the downward, water-filled hole by force ofgravity, the prongs and leaf springs, normally cambered or biased radially outward, are flexed radially inward by contact with the inside wall of the outer tube 22 counter to the outward camber bias of the leaf springs. Thus, the only part of the prongs and the springs that touches the inside surface of the drill string, as the core barrel assembly is gravity displaced relative to the drill string, and the curved exterior surfaces of the cams 130. Each cam 130 may be provided with one or more surface-exposed tungstencarbide buttons (not shown) or the like to prevent excessive wear.

A second basic purpose of each cam 130 is to prevent wear on the adjacent coupling ridge 132, which is separated from the cam 130 in the embodiment of FIG. 4 by an arcuate groove 1341, each disposed at the exterior surface of the prong 92. In the drilling position, each cam 130, of the four illustrated prongs 92, is disposed within the annular recess 32 previously mentioned. This disposition accommodates close coupling of the ridge 132 within the upper two-way coupling annular recess 30.

The coupling ridge 132 couples directly with the outer tube, not necessitating a third piece suspension device, and comprises an arcuate mating surface 136, an upper-coupling surface 138 and a lower-coupling surface 140. The upper coupling surface 138 achieves fail-safe coupling with the upper surface of the recess against rearward release during drilling regardless of whether the drilling is with or counter to gravity. This makes the weight of the core barrel assembly an uninfluential factor in uncoupling the core barrel assembly from the outer tube, contrary to the prior art.

The lower-coupling surface N0 of the ridge 132 provides fail-safe coupling against forward release of the core barrel assembly in the direction of the bit. Thus, damage to the rotating bit and wear to the normally stationary shoe dd are essentially obviated because the bit and shoe are not brought together by pressure force of the downward circulating water, which water is conventionally used to cool the bit during drilling. It should be appreciated that approximately 800 percent greater outer tube coupling surface area is provided using the described features of this invention as compared with present commercially accepted core barrel assemblies.

The distal end of each prong 92 comprises a spearhead hook 146 having an exterior tapered surface 148 and an overshot latching shoulder 150. The shoulder 150 is separated from the adjacent coupling ridge 132 by an arcuate groove 152 disposed in each prong. Inspection of FIG. d shows that, during drilling, the transverse position of each spearhead hook 146 is spaced from the inner wall of the outer tube 22.

The tapered surface 148 of each prong 92 accommodates inward radial gathering or clustering of the prongs when the overshot 02 is advanced toward the end of the hole 26 and brought in contact with the tapered surface 148 of each prong during such advance. The inward gathering of the prongs toward the radial center line of the core barrel assembly thereafter accommodates further displacement of the overshot along the tapered surface 148 of each prong, thereby first radially uncoupling the coupling ridge 132 from the annular recess 30, and thereafter latching the overshot upon the shoulder 150 of each prong. The advance of the overshot is then discontinued and the overshot and the core barrel assembly (with the trapped core) are retrieved from the hole. In this way, it is not necessary or possible to first latch the overshot to the core barrel assembly before ascertaining whether or not the core barrel assembly can in fact be uncoupled from the outer tube. Also, by utilization of a plurality of prongs with overshot latching hooks 150, approximately 300 percent greater overshot latching surface area is provided than with commercial prior art spearhead configurations. Hence, the probability of shear failure of the spearhead during overshot retrieval of a core barrel assembly is significantly diminished, if not prohibited.

THE OVERSHOT OF FIGS. 6-10 The overshot 52 of FIGS. 6-10 is useful not only for removing novel core barrel assemblies of the type previously described from coupling relation with the drill string but also for overshot placing the core barrel assembly in a dry hole without risk of inadvertent release of the core barrel assembly and damage to the bit. The overshot is also useful, when disabled, as an accelerated weight to place a core barrel assembly and in coupled relation with a downwardly extending outer tube ofa drill string, when the drill string is filled with water.

Structurally, with special reference: to FIGS. 6 and 7, the overshot 52 comprises a shoe having a bell-shaped recess 162 disposed near the bottom opening 164. A short distance above the opening 164 exists an annular core barrel assembly latching shoulder 166 which extends in the illustrated embodiment through the entire 360 of the inside circumference of the recess 162. The central interior of the shoe 160 comprises a cylindrically hollow counterbore 168 terminating in an abutment surface 170 and opening not only into recess 162 but also into an elongated bore 172 which extends upwardly. The bore 172 comprises the inside surface of an upper telescopic, reduced diameter portion 174 of shoe 160. The cylindrical telescopic portion 174 contains an L-shaped slot having a downwardly extending leg 176 and a circumferentially extending leg 175.

The upper end of the reduced diameter cylindrical portion 174 is solid at 178 and contains a diametrical bore 180 through which a pin 182, having enlarged ends 184, passes.

A plunger is concentrically disposed inside the shoe 160. The plunger 190 comprises a spool head 192 having a frustoconical recess 194 and a reload slot 196 disposed at the top wall 198 of the recess 194. A cylindrically shaped integral stern 200 extends upwardly from the concentric to the spool head 192 and is slidably and rotationally disposed within the bore 172 of shoe 1160.

A release spring 202 functions as a combined torsion and compression spring between the shoe abutment surface 17. and the top spool surface 204. The ends 206 and 208 are respectively anchored in anchor recesses 210 and 212 at surfaces 170 and 204. Thus, a two-way bias is provided, i.e., (a) bias of the plunger axially toward the shoe latching shoulder 166 and (b) bias of the plunger rotationally right to left, as viewed in the Figures.

The plunger 190 is normally retained in the retracted (enabling) position illustrated in FIGS. 7 and 8 counter to the mentioned axial bias. Provision is made for release of the plunger 190 to an extended (disabling) position (FIG. 9) due to the bias of the spring 202 in a manner subsequently to be described.

An open groove 220 is provided in the top of stem 200, which groove extends essentially diametrically and is provided with a threaded bore (not shown) in which a bolt 222 is securely fastened. The bolt 222 passes through an aperture (not shown) in a locking plate 224 and through an aperture (not shown) in a release dog or release pawl 226 to integrally unite the pawl 226 with the stem 220 and thereby insure joint movement of the plunger 190 and the pawl 226.

The pawl 226 passes through the previously mentioned L- shaped slot in the upper end 174 of the shoe 160, the pawl being disposed in the circumferentially extending portion of the slot 175 when the plunger 190 is in the retracted position (FIGS. 7 and 8) and in the downwardly extending leg 176 (FIG. 7) of the L-shaped slot when the plunger 190 is disposed in its extended position (FIG. 9). Thus, the disposition of the pawl in the L-shaped slot in telescopic cylindrical portion 174 accommodates both plunger rotation in the circumferentially extending slot leg 175 and axial displacement of the plunger in the downwardly extending slot leg 176.

The overshot 52 also comprises a release housing, generally designated 230. The release housing 230 has a threaded axial bore 232 adapted to threadedly couple with a wire line coupling member 233 (FIG. 2) to which a wire line or cable is conventionally secured. The release housing 230 has a stop shoulder 234 near which the solid end 178 of the shoe 160 is disposed when the release housing 230 is in its downwardmost relative position as viewed in the Figures. Oppositely disposed pin slots 236 are fabricated in the walls of the release housing 230 near the top of the bore 238 and each slot receives one of the two enlarged pin ends 184 so as to accommodate a limited amount of up and down movement of the release housing corresponding to the length of the slot 236 for purposes which will become more fully apparent subsequently.

A plurality of top and bottom teeth, 240 and 242 respectively, exist along a circumferentially extended portion of the release housing slightly below the pin slots 236. EAch top tooth is offset relative to the adjacent bottom teeth and vice versa. The top teeth are spaced from each other by a predetermined distance represented by a recess 244, as are the bottom teeth. The array of teeth 240 and 242 terminates in a downwardly extending release slot 246. The circumferential portion of the release housing occupied by the teeth 240 and 242 is coextensive with and concentric to the circumferential leg 175 ofthe mentioned L-shaped slot in the upper telescopic portion 174 of the shoe 160. Likewise, the release slot 246 is coextensive and radially aligned with the downwardly extending leg 176 of the mentioned L-shaped slot.

With the foregoing in mind and assuming an orientation wherein the plunger 190 is disposed in its retracted position as shown in FIGS. 7 and 8 and with the overshot 52 suspended from a wire line, the pin 182 will be oriented so that the enlarged ends 184 will be disposed in the bottom of the adjacent slot 236 due to the weight force of the plunger and shoe. In this position, up and down pumping of the wire line by the operator will shift the release housing up and down through the distance permitted by the pin slots 236. This will first shift the pawl, which is biased left to right by the spring 202, to the right surface of the next top tooth 240 (on the down stroke of the release housing) and then to the right surface of the next bottom tooth 242 (on the up stroke of the release housing).

Hence, when and if the operator desires, the up and down pumping may be continued to successively move the pawl right to left across the requisite number of teeth, top and bottom, so that the pawl thereafter becomes disposed in the release slot 246 accommodating movement of the plunger 190 from the retracted position (FIGS. 7 and 8) to the extended position (FIG. 9) under force of the spring 202. In the extended position, the spool 192 shields the shoe-latching shoulder 166 against prong latching. The effects of so extending the plunger 190 are, therefore, (a) to release the prongs 92 from the overshot in the hole at the operator's will, such as then the core barrel assembly is being placed in coupled relation with the outer tube and the hole is dry, and/or (b) to prevent subsequent latching between the overshot at shoulder 166 and the prong spearhead latching shoulders 150. Also, with the plunger extended in a disabling position, the overshot may be utilized as an accelerating weight when downwardly placing the core barrel assembly in coupled relation with the outer tube when the hole is substantially filled with water;

As illustrated in FIG. 10, once the overshot and the latched core barrel assembly have been retrieved from the hole to the surface, the overshot may easily by manually separated from the prongs simply by angularly rotating the overshot relative to the prongs so that the centerlines of the two components are obliquely related. The prongs are thus gathered toward the longitudinal center line of the core barrel assembly and the shoulders are displaced out of latching engagement with the annular shoulder 166 of the overshot. Thereafter the overshot and prongs are parted.

To return the plunger from the extended position of FIG. 9 to the retracted position illustrated in FIGS. 7 and 8, once the overshot has been returned to the surface, it is merely necessary for the operator to place a suitable tool, such as a screwdriver, in the reload slot 196 and thereafter exert an axial force sufficient to overcome the axial bias of the spring 202 and shift the pawl 226 to the top of release slot 246. Thereafter, while maintaining such axial force, a rotational force sufficient to overcome the torque exerted by spring 202 is exerted by the tool upon the plunger-190 as the release housing 230 is shifted to and fro, a suitable number of times, through the distance allowed by pin slot 236. In this way, the release pawl 226 will be displaced sinuously through the array of top and bottom teeth 240 and 242 left to right until the pawl 226 is disposed at the right side of whichever tooth is desired, at which time the axial and rotational force exerted by the tool will be withdrawn. The torque force of the spring will hold the pawl 226 in such position against the right side of the next left tooth so long as the release housing 230 is not pumped up and down. The operator may select to position the pawl against any desired tooth depending on how many up and down pumping motions in the hole may subsequently be deemed sufficient for later displacement of the plunger 190 into the extended position of FIG. 9, as previously explained.

OVERSHOT EMBODIMENT OF FIGS. 11-13 Reference is now made to FIGS. 11-13 which depict a second presently preferred overshot, generally designated 310, utilized for coupling with and uncoupling from a conventional core barrel assembly spearhead 312 having a latching shoulder 314. Certain portions of the overshot 310 are substantially identical to components of the previously described overshot 52 and are correspondingly numbered. These include the release housing 230, the cylindrical telescopic portion 174, the plunger stem 200 and the torsion-compression spring 202.

The appreciable differences between the overshot 310 and the overshot 52 include the plunger head 316 which has a conical tapered surface at distal end 318 and a reload slot 320, fashioned at the tip of the conical end 318. The cylindrical portion 174 is preferably threadedly coupled at 322 to a spearhead latching mechanism, generally designated as 324.

The latch mechanism 324 comprises a plurality of radially yieldable depending fingers 326, preferably formed of spring steel. Each finger has a tapered conical surface 328 closely spaced from the surface of the conical end 318 of the plunger head 316 when the plunger is retracted. Each finger 326 also comprises a spearhead receiving recess 330 which terminates in a latching shoulder 332. Each latching shoulder 332 constitutes part of a spearhead hook 334 which also includes a tapered surface 336. The surface 336 accommodates spreading ofthe radially yieldable fingers 326 when the overshot 310 is advanced against the upper tapered cone of the spearhead 312 to latch the shoulders 332 of the overshot 310 under the annular shoulder 314 of the conventional spearhead 312 (FIG. 11).

It) I (l l 4 0209 The operation of the overshot 310 is essentially the same as the previously described operation of the overshot 52 except the standard core barrel assembly, of which spearhead 312 is a part, will be uncoupled from the outer tube on the up stroke of the overshot after latching between the spearhead 312 and the overshot 310. Thus, when the wire line operator pumps the release housing 230 a sufficient number of times to dispose the release pawl 226 in the release slot 246 (FIGS. 6 and 7) the plunger will move from the retracted position of FIG. 13 to the extended position of FIG. 13 bringing the surface of the conical end 318 into forcible contact with the tapered conical surfaces 328 of the radially yieldable fingers 326 spreading the fingers to create a space between the two hooks 334 which is greater than the diametrical distance across the shoulder 314. Hence, the conventional spearhead can be released in this way at thewill of the wire line operator.

To reload the plunger 316 from the extended position of FIG. 13 to the retracted position of FIG. 11, a suitable tool, such as a screw driver, is placed in the reload slot 320 and an axial force is exerted through the tool sufficient to overcome the axial bias of spring 202 and displace the release pawl 226 to the top of the release slot 246. Thereafter, while maintaining the axial force of the tool a rotational force is exerted left right upon the plunger as the release housing is moved to and fro until the release dog is positioned at the right side of whichever tooth is desired, at which time the tool is removed.

OVERSHOT EMBODIMENT OF FIG. 14

Where it is important to reduce frictional resistance of the overshot components to rotational displacement of the pawl 226 from tooth-to-tooth responsive to down and up displace ment of the wire line, the overshot of FIG. M may be effectively employed. The overshot of FIG. 14 may be identical in structure and operation to either of the two previously described overshots 52 and 310 except for the toothed construction of release housing 350 (FIG. M).

Release housing 350 comprises an array of spaced upper teeth 352 and an array of spaced lower teeth 354, each upper tooth being located intermediate spaced bottom teeth in offset relation, and vice versa. The right surface 360 (as viewed in FIG. 14) of each top tooth 352 extends linearly in a generally vertical each as does the right surface 362 of each bottom tooth 354. Thus, the pawl 226 may flatly and forcibly abut such right tooth surfaces 360 and 362 sequentially responsive to the torsional bias of the overshot spring as the release housing 350 is displaced own and up by the wire line.

The left ramp surface 356 of each top tooth 352 extends curvilinearly from the distal end of one top tooth to the proximal attachment of the next left top tooth at the right surface 360 thereof. Similarly, the left ramp surface 358 of each bottom tooth 354 extends curvilinearly from the distal end of one bottom tooth to the proximal attachment of the next left bottom tooth at the right surface 326,

Thus, assuming the plunger of the overshot to be retracted llll;

and upon dropping the wire line-suspended release housing 350 relative to the remainder of the overshot, the pawl 226 will be relatively displaced by the torsion spring from the right side 362 of one bottom tooth to the right side 360 of the next left adjacent top tooth traversing the opposite ramp surface 356 with a minimum of friction where resistance to such pawl movement is substantial, as when a fluid other than water, having a relatively heavy viscosity, is used as a cooling fluid and/or where there is an appreciable amount of sand or the like in the fluid near the bottom of the hole. In like manner, subsequent upward displacement of release housing 350 relative to the remainder of the overshot will displace the pawl 226 from biased contiguous relation with the right surface 360 of the top tooth to biased contiguous relation with the right surface 362 of the next left adjacent bottom tooth across the opposed ramp surface 353, where said substantial resistance exists.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. A method of handling a core barrel assembly comprising: latching an overshot to the upper end of said assembly by means of a latch means having a contracted latching position and an expanded unlatched position, said overshot having a plunger and means for extending said plunger from the overshot to a position holding the latch means in its expanded position in response to pumping a predetermined number of times a wire line to which the overshot is attached, lowering said overshot and assembly on a wire line into a drill string to a position where the assembly can couple to the string, extending said plunger by pumping the wire line said predetermined number of times to release the overshot from the assembly, and withdrawing the overshot from the string.

2. The method as defined in claim I. wherein the plunger is thereafter returned to a retracted position by axially forcing retraction of the plunger counter to a resilient axial bias and thereafter rotationally displacing the plunger counter to a resilient rotational bias while axially shifting a plurality of stop positions to and fro, and releasably restraining the plunger counter to each said bias at a selected stop position.

3. A method as defined in claim 2 wherein all but the last said pumping steps rotationally shifts said plunger between stop positions in the direction of said resilient rotational bias and said last pumping step axially shifts said plunger from the retracted to the incapacitated extended position in the direction of said axial bias. 

2. The method as defined in claim 1 wherein the plunger is thereafter returned to a retracted position by axially forcing retraction of the plunger counter to a resilient axial bias and thereafter rotationally displacing the plunger counter to a resilient rotational bias while axially shifting a plurality of stop positions to and fro, and releasably restraining the plunger counter to each said bias at a selected stop position.
 3. A method as defined in claim 2 wherein all but the last said pumping steps rotationally shifts said plunger between stop positions in the direction of said resilient rotational bias and said last pumping step axially shifts said plunger from the retracted to the incapacitated extended position in the direction of said axial bias. 